linux-kernel - Re: [PATCH 1/4] dt-bindings: clock: meson: update documentation with hhi syscon

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Date:   Thu, 22 Mar 2018 22:04:13 -0500
From:   Rob Herring <robh@...nel.org>
To:     Jerome Brunet <jbrunet@...libre.com>
Cc:     Kevin Hilman <khilman@...libre.com>,
        Neil Armstrong <narmstrong@...libre.com>,
        Carlo Caione <carlo@...one.org>,
        linux-amlogic@...ts.infradead.org,
        linux-clk <linux-clk@...r.kernel.org>,
        devicetree@...r.kernel.org,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "moderated list:ARM/FREESCALE IMX / MXC ARM ARCHITECTURE" 
        <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH 1/4] dt-bindings: clock: meson: update documentation with
 hhi syscon

On Sun, Mar 18, 2018 at 10:09 AM, Jerome Brunet <jbrunet@...libre.com> wrote:
> On Sun, 2018-03-18 at 07:52 -0500, Rob Herring wrote:
>> On Thu, Mar 15, 2018 at 12:55:42PM +0100, Jerome Brunet wrote:
>> > The HHI register region hosts more than just clocks and needs to
>> > accessed drivers other than the clock controller, such as the display
>> > driver.
>> >
>> > This register region should be managed by syscon. It is already the case
>> > on gxbb/gxl and it soon will be on axg. The clock controllers must use
>> > this system controller instead of directly mapping the registers.
>>
>> Sounds like a kernel problem, not a DT one.
>
> It's a platform problem, so it has much a kernel problem (solution already
> merged) as a DT problem
>
> DT wise, we've got two devices mapping the same region
>
> in arch/arm64/boot/dts/amlogic/meson-gx.dtsi:
>> system-controller@0
>
> which is used by the display device.
>
> and in arch/arm64/boot/dts/amlogic/meson-gxbb.dtsi (same for gxl)
>> clock-controller@0
>
> It has worked so far because the clock controller claims the region w/o
> reserving it but it remains unsafe since both device may access the same region.
> The fix is to have the clock controller go through the existing syscon.

We certainly want to avoid multiple nodes using the same mmio region.


>> With a single child, there is really no point to this change. A single
>> node can provide multiple functions. Look at nodes that are both reset
>> and clock providers.
>
> There is more than a single user, as explained above and in the cover letter of
> this series.

Right, but a single node can support more than a single user (or
provider). You don't have to have multiple nodes to have multiple
users/providers.

Rob